The present invention relates to a method and device for controlling a spark-ignition direct injection engine.
In order to increase a heat efficiency of an engine to improve fuel consumption, it is effective to increase a compression ratio. However, with a spark-ignition engine using gasoline or a fuel containing gasoline, if a compression ratio is high in which a geometric compression ratio is above 12:1, within an operating range where an engine speed is comparatively low and an engine load is high, abnormal combustion such as knocking and pre-ignition (hereinafter, the abnormal combustion is represented by “knocking”) are easily caused. As one of measure to suppress such knocking, retarding an ignition timing greatly may be proposed.
For example, JP2010-101312A discloses a control in a spark-ignition direct injection engine with a high compression ratio, which suppresses an occurrence of knocking within a low speed range where the engine load is high, where knocking easily occurs, by performing divided injections in which an injection of a small amount of fuel is performed in an intake stroke and an injection of a large amount of fuel is performed in a late stage of compression stroke, in addition to greatly retarding an ignition timing to after top dead center on the compression stroke.
However, although the suppression of knocking can be expected with the above control, a sufficient torque cannot be secured therewith. That is, although a high compression ratio engine has a potential of having an increased torque, a sufficient torque has not conventionally been achieved due to countermeasures against knocking.